1. Technical Field
The present invention relates to a near field light generating element configured to collect an induced luminous flux and generate a near field light from the luminous flux, a near field optical head configured to record various information in a magnetic recording medium at a super-high density utilizing the near field light generated by the near field light generating element, and an information recording and reproducing apparatus having the near field optical head.
2. Background Art
In recent years, the recording density of information in a single recording plane is increased in association with increase in capacity of a hard disk or the like in computer equipment. For example, in order to increase the recording capacity per unit area of a magnetic disc, it is necessary to increase the surface recording density. However, in association with increase in recording density, the recording area per one bit on a recording medium is reduced. When the bit size is reduced, the energy possessed by one bit information becomes close to the heat energy of ambient temperatures, and hence a problem of heat demagnetization such as recorded information is inverted or lost due to heat fluctuations or the like arises.
Although a generally used in-plane recording system is a system to record magnetism so as to cause the direction of magnetization to direct toward the in-plane direction of the recording medium, with this system, the above-described loss of the recorded information or the like due to the heat demagnetization is apt to occur. Therefore, in order to solve such inconveniences, it is in the course of transferring to a perpendicular (vertical) recording system which records magnetizing signals in the direction vertical to the recording medium. This system is a system in which magnetic information is recorded on the basis of a principle to bring a single magnetic pole to the recording medium. According to this system, a recording magnetic field is directed substantially vertical to a recording film. Information recorded in the vertical magnetic field is easy to maintain its energetic stability since an N-pole and an S-pole can hardly generate a loop in the recording film plane. Therefore, this perpendicular recording system is resistive against the heat demagnetization in comparison with the in-plane recording system.
However, the recording medium in recent years is required to have a higher density in response to a need such that recording and reproduction of a larger amount of higher density information or the like is desired. Therefore, the recording medium having a higher coercivity are started to be employed in order to minimize influences between adjacent magnetic domains or the heat fluctuations. Therefore, even with the above-described perpendicular recording system, recording of information in the recording medium becomes difficult.
Therefore, in order to solve this inconvenience, a hybrid magnetic recording system (near field light assisted magnetic recording system) in which the magnetic domain is locally heated by the near field light to lower the coercivity temporarily to allow writing during this period is proposed. This hybrid magnetic recording system is a system utilizing a near field light generated by a mutual action between a minute area and an optical aperture formed on the near field optical head in a size not exceeding the wavelength of the light. In this manner, by utilizing the minute optical aperture exceeding a diffraction limited of the light, that is, the near field optical head having the near field light generating element, handling of optical information in an area not exceeding the wavelength of the light, which has been considered to be limited in the optical system in the related art, is enabled. Therefore, the high-density of a recording bit exceeding the light information recording and reproducing apparatus or the like in the related art is achieved.
The near field light generating element is not limited to the optical minute aperture described above, and may be configured with a projecting portion formed, for example, in manometers. With such the projecting portion, generation of the near field light is achieved in the same manner as the optical minute aperture.
Although various types of writing heads on the basis of the hybrid magnetic recording system described above are provided, as one of those, a near field optical head in which the increase in recording density is achieved by reducing the size of a light spot is known (for example, see JP-A-2004-158067 and JP-A-2005-4901).
This near field optical head mainly includes a main magnetic pole, an return pole (auxiliary magnetic pole), a coil winding having a helical conductive pattern formed in the interior of an insulator, a metal scatterer configured to generate a near field light from an irradiated laser beam, a plane laser light source configured to irradiate the metal scatterer with the laser beam, and a lens configured to focus the irradiated laser beam. These respective components are attached to a side surface of a slider fixed to a distal end of the beam.
The main magnetic pole has a surface opposing the recording medium on one end side, and is connected to the return pole on the other end side. In other words, the main magnetic pole and the return pole constitute a single magnetic poly type vertical head having one magnetic pole (single magnetic pole) arranged in the vertical direction. The coil wining is fixed to the return pole in such a manner that part of it passes between the magnetic pole and the return pole. The magnetic pole, the return pole, and the coil winding as described above constitute an electromagnet as a whole.
The above-described metal scatterer formed of gold or the like is attached to a distal end of the main magnetic pole. The above-described plane laser light source is arranged at a position apart from the metal scatterer and the above-described lens is arranged between the plane laser light source and the metal scatterer.
The respective components as described above are attached in the order of the return pole, the coil winding, the main magnetic pole, the metal scatterer, the lens, and the plane laser light source in sequence from the side of the side surface of the slider.
When utilizing the near field optical head configured in this manner, various information is recorded in the recording medium by applying the recording magnetic field simultaneously with the generation of the near field light.
In other words, the laser beam is applied from the plane laser light source. This laser beam is focused by the lens and is applied on the metal scatterer. Then, since free electrons in the interior of the metal scatterer are uniformly oscillated by the electric field of the laser beam, a plasmon is excited so that the near field light is generated at a distal end portion. Consequently, a magnetic recording layer of the recording medium is locally heated by the near field light, and the coercivity is temporarily lowered.
Also, by supplying a drive current to the conductive pattern of the coil winding simultaneously with the above-described laser beam irradiation, the recording magnetic field is locally applied on the magnetic recording layer of the recording medium close to the main magnetic pole. Accordingly, recording of various information in the magnetic recording layer in a state in which the coercivity is temporarily lowered is achieved. In other words, the recording in the recording medium is achieved in cooperation between the near field light and the magnetic field.    Patent Document 1: JP-A-2004-158067    Patent Document 2: JP-A-2005-4901
However, the near field optical head in the related art as described above still has the following problem.
In other words, when generating the near field light which is inevitable in information recording, the metal scatterer is irradiated with the laser beam from the plane laser light source via the lens. However, since the metal scatterer is attached to the distal end of the main magnetic pole, the laser beam is obliged to be applied obliquely from the plane laser light source. Therefore, the laser beam cannot be entered along the metal scatterer and hence the laser beam is lost on the way by scattering or the like, so that efficient generation of the near field light is difficult. In particular, since the metal scatterer is not able to systematically change the direction of introduced light, it is obliged to irradiate the metal scatterer with the laser beam obliquely to cause the same to enter therein described above.
Also, since the lens is needed to be arranged between the plane laser light source and the metal scatter while considering the interference with the recording medium, the one having a semi-circular shape is used. Therefore, it is difficult to focus the laser beam on the metal scatterer with a high degree of efficiency. This also causes the lowering of the near field light generation efficiency.